LOANS RECEIVABLE AND THE ALLOWANCE FOR CREDIT LOSSES (Loans by Type) (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Jun. 30, 2023	Dec. 31, 2022	Sep. 30, 2022	Jun. 30, 2022	Dec. 31, 2021
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases Receivable, Gross	$ 10,611,417		$ 10,146,724
Allowance for credit losses - loans	(146,960)	$ (144,680)	(141,465)	$ (135,918)	$ (128,702)	$ (132,099)
Net loans	$ 10,464,457		$ 10,005,259
Percent of total loans	100.00%		100.00%
Unearned loan fees in excess of unamortized costs	$ 11,200		$ 8,100
Discount on acquired loans, net	5,100		6,600
Financing Receivable, Accrued Interest, before Allowance for Credit Loss	45,500		39,800
Financing Receivable, Loans Held as Collateral, FHLB and Other Borrowings	7,200,000
Commerical real estate - owner-occupied [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases Receivable, Gross	$ 911,540		$ 845,320
Percent of total loans	8.60%		8.30%
Commercial real estate - investment properties
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases Receivable, Gross	$ 1,530,087		$ 1,589,975
Percent of total loans	14.40%		15.70%
Small Balance Commercial Real Estate Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases Receivable, Gross	$ 1,169,828		$ 1,200,251
Percent of total loans	11.00%		11.80%
Multifamily Real Estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases Receivable, Gross	$ 766,571		$ 645,071
Allowance for credit losses - loans	$ (8,804)	(8,039)	$ (7,734)	(7,114)	(6,906)	(7,043)
Percent of total loans	7.20%		6.40%
Commercial construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases Receivable, Gross	$ 168,061		$ 184,876
Percent of total loans	1.60%		1.80%
Multifamily construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases Receivable, Gross	$ 453,129		$ 325,816
Percent of total loans	4.30%		3.20%
One- to four- family construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases Receivable, Gross	$ 536,349		$ 647,329
Percent of total loans	5.10%		6.40%
Land and land development
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases Receivable, Gross	$ 346,362		$ 328,475
Percent of total loans	3.30%		3.20%
Commercial Business
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases Receivable, Gross	$ 1,263,747		$ 1,283,407
Percent of total loans	11.90%		12.70%
Loans And LeasesReceivable Gross Carrying Amount, SBA Paycheck Protection Program	$ 4,100		$ 7,600
Small business scored
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases Receivable, Gross	$ 1,000,714		$ 947,092
Percent of total loans	9.40%		9.30%
Agricultural business, including secured by farmland
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases Receivable, Gross	$ 334,626		$ 295,077
Allowance for credit losses - loans	$ (3,718)	(3,573)	$ (3,475)	(3,455)	(3,002)	(3,190)
Percent of total loans	3.10%		2.90%
Loans And LeasesReceivable Gross Carrying Amount, SBA Paycheck Protection Program	$ 0		$ 334
One- to four-family residential [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases Receivable, Gross	1,438,694		1,173,112
Allowance for credit losses - loans	$ (17,925)	(16,737)	$ (14,729)	(12,394)	(9,573)	(8,205)
Percent of total loans	13.60%		11.60%
Consumer—home equity revolving lines of credit
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases Receivable, Gross	$ 579,836		$ 566,291
Percent of total loans	5.40%		5.60%
Consumer-other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases Receivable, Gross	$ 111,873		$ 114,632
Allowance for credit losses - loans	$ (9,043)	$ (8,971)	$ (8,971)	$ (8,751)	$ (7,236)	$ (6,951)
Percent of total loans	1.10%		1.10%